(1) Field of the Invention
The present invention relates to the field of valve controllers in systems and methods, and fuel injection systems utilizing the same.
(2) Prior Art
Fuel injectors are used to introduce pressurized fuel either directly into the combustion chamber of an internal combustion engine or, alternatively, into the intake manifold adjacent to the inlet valve of each cylinder. FIG. 1 shows a fuel injection system 10 of the prior art as used for diesel injection directly into the combustion chamber of a diesel engine. The injection system includes a nozzle 12 that is coupled to a fuel port 14 through an intensifier chamber 16. The intensifier chamber 16 contains an intensifier piston 18 which reduces the volume of the chamber 16 and increases the pressure of the fuel therein. The pressurized fuel is released into a combustion chamber through the nozzle 12.
The intensifier piston 18 is stroked by a working fluid that is controlled by a poppet valve 20. The working fluid enters the valve through port 22. The poppet valve 20 is coupled to a solenoid 24 which can be energized to pull the valve into an open position. As shown in FIG. 2, when the solenoid 24 opens the poppet valve 20, the working fluid applies a pressure to the intensifier piston 18. The pressure of the working fluid moves the piston 18 and pressurizes the fuel. When the solenoid 24 is deenergized, springs 26 and 28 return the poppet valve 20 and the intensifier piston 18 back to the original positions.
Spring return fuel injectors are relatively slow because of the slow response time of the poppet valve return spring. Additionally, the spring rate of the spring generates an additional force which must be overcome by the solenoid. Consequently the solenoid must be provided with enough current to overcome the spring force and the inertia of the valve. Higher currents generate additional heat and degrade the life and performance of the solenoid. Furthermore, the spring rate of the springs may change because of creep and fatigue. The change in spring rate will create varying results over the life of the injector.
Conventional fuel injectors typically incorporate a mechanical feature which determines the shape of the fuel curve. Mechanical rate shapers are relatively inaccurate and are susceptible to wear and fatigue. Additionally, fuel leakage into the spring chambers of the nozzle and the intensifier may create a hydrostatic pressure that will degrade the performance of the valve.
The graph of FIG. 3 shows an ideal fuel injection rate for a fuel injector. To improve the efficiency of the engine, it is desirable to pre-inject fuel into the combustion chamber before the main discharge of fuel. As shown in phantom, the fuel curve should ideally be square so that the combustion chamber receives an optimal amount of fuel. Actual fuel injection curves have been found to be less than ideal, thereby contributing to the inefficiency of the engine. It is desirable to provide a high speed fuel injector that will supply a more optimum fuel curve than fuel injectors in the prior art.
As shown in FIGS. 1 and 2, the poppet valve constantly strikes the valve seat during the fuel injection cycles of the injector. Eventually the seat and the poppet valve will wear, so that the valve is not properly seated within the valve chamber. Improper valve seating may result in an early release of the working fluid into the intensifier chamber, causing the injector to prematurely inject fuel into the combustion chamber. It would be desirable to provide an injector valve that did not create wear between the working fluid control valve and the associated valve seat of the injector.
The solenoid 24 of the fuel injector of FIGS. 1 and 2 is a. direct pull solenoid operating in opposition to spring 26. This is an advantage over still earlier prior art fuel injectors which were cam operated in that the solenoid operated injectors of FIGS. 1 and 2 may be electronically controlled in timing and duration, unlike the cam operated injectors wherein at least the initiation of injection was typically at a fixed angle of rotation of the crankshaft independent of engine speed or load. The solenoid operated injectors of FIG. 1 and 2 have the disadvantage however, of not being as fast as they could be, and of consuming more power than necessary. In particular, since the solenoids operate in opposition to spring 26, the net force controlling the speed of opening of the poppet valve 20 is not the solenoid force, but rather the difference between the solenoid force and spring force 26, whereas the net force closing the valve is simply the spring force 26, which can only be a fraction of the solenoid opening force for the valve to operate. Accordingly, the full pulling potential of the solenoid is not realized on either opening or closing of the poppet valve. Also, the solenoid must remain energized for as long as the solenoid is actuated, and thus must be of a size and of a heat dissipation capability commensurate with a "full throttle" fuel injection rate. Further, the solenoid pulling force must be adequate to properly operate the valve at the lower extreme of the power supply and upper extremes of solenoid coil resistance, the force of spring 26, etc., while at the same time not overheating at full throttle, upper power supply voltage and low solenoid coil resistance extremes. It is the improvement of performance in this area, among other things, to which the present invention is directed.